Apparatus and method for vaporizing molten metal

ABSTRACT

Apparatus and method for vacuum vaporization of molten metal without entrainment of liquid droplets includes charging a pool of molten metal into a first cylinder member which has its central axis disposed horizontally and has at least one passage therethrough. A second cylinder member, also having its central axis disposed horizontally, encloses the first cylinder member so as to receive molten metal through the passage. A thin semicylindrical shell of fluid metal is thus formed between the cylinder members. Heating the thin shell generates metal vapor. The metal vapor is passed through a tortuous path to remove any liquid droplets, and is discharged from an outlet nozzle for deposition upon a substrate. In a modification the molten metal is contained in the lower portion of an evaporator member. A shelf with a passage therethrough divides the evaporator member horizontally while allowing generated metal vapor to pass to the upper portion of the evaporator member. There the vapor is passed through a tortuous path to remove any liquid droplets, thence proceeding to an outlet nozzle for deposition upon a substrate.

United States Patent 1 9 ,638 Roblin et al. [451 Sept. 12, 1972 [54] APPARATUS FOR VAPORIZING [72] Inventors: John M. Roblin, Cleveland; Frank J. Cole, Parma; William A. Reed, West Richfield, all of NJ. [73] Assignee: Republic Steel Corporation Cleveland, Ohio [22] Filed: May 15, 1970 [21] Appl. No.: 37,703

[52] US. Cl. ..266/34 R, 117/107, 118/49 [51] Int. Cl ..C21c 7/00 [58] Field of Search ..118/48, 49, 49.1, 49.5; 117/107, 107.1; 266/34 R, 39

[56] References Cited UNITED STATES PATENTS 231,038 8/1880 I-Iarris ..118/48 2,879,739 3/1959 Bugbee et al. ..118/49 3,210,525 10/1965 Liben ..118/49 3,278,331 10/1966 Taylor et al. ..118/49 3,356,529 12/1967 Kiser et a1 ..118/49 3,514,575 5/1970 Hall et al. ..1l8/49.5

FOREIGN PATENTS OR APPLICATIONS 766,119 I/1953 Great Britain ..118/49 MOLTEN METAL Primary Examiner-Gerald A. Dost Attorney-Robert P. Wright and Joseph W. Malleck 57f l ABSTRACT Apparatus and method for vacuum vaporization of molten metal without entrainment of liquid droplets includes charging a pool of molten metal into a first cylinder member which has its central axis disposed horizontally and has at least one passage therethrough. A second cylinder member, also having its central axis disposed horizontally, encloses the first cylinder member so as to receive molten metal through the passage. A thin semi-cylindrical shell of fluid metal is thus formed between the cylinder members. Heating the thin shell generates metal vapor. The metal vapor is passed through a tortuous path to remove any liquid droplets, and is discharged from an outlet nozzle for deposition upon a substrate.

In a modification the molten metal is contained in the lower portion of an evaporator member. A shelf with a passage therethrough divides the evaporator member horizontally while allowing generated metal vapor to pass to the upper portion of the evaporator member. There the vapor is passed through a tortuous path to remove any liquid droplets, thence proceeding to an outlet nozzle for deposition upon a substrate.

22 Claims, 9 Drawing Figures PATENTEDSEP12 I912 3.690.638

sum 2 OF 3 INVENTORS JOHN M. EOBL/AJ FRANK J. COLE BY W/LL/AM A. E E0 APPARATUS AND METHOD FOR VAPORIZING MOLTEN METAL BACKGROUND OF THE INVENTION This invention relates to vaporizing molten metal, particularly zinc, while preventing liquid droplets from being entrained in the metal vapor.

vaporized zinc coatings on steel offer many advantages over conventional electroplated zinc coatings and hot dip galvanized coatings. A smooth coating can be produced by vapor deposition while coating thickness can be varied by controlling thezinc evaporation rate and/or the speed of a moving steel substrate to be coated. A one-side coating can be easily produced by properly shielding the strip. Composite coatings, e.g., a thin aluminum coating over a thin zinc coating, can be produced by vapor deposition, the steel thus coated having excellent corrosion resistance. Production speed canbe considerably fasterfor vapor deposition than for an electroplating line ora hot dip .gal-

vanizing line because therestrictions of current density and coating roll speed do notapply. There is no inherent limitation on the gage of steel that might be coated, and is unlike galvanizing lines whereline speed must belowered as thickness and/or width of the strip is increased in order to allow for increased heat demand on the galvanizing pot. Furthermore, the cost of vapor deposition is believed to be less than the cost of either electroplating or hot dip galvanizing.

Traditionally, metals have been evaporated from crucibles simply by heating the metal to a temperature above its vaporization point and then removing the vapor from the crucible, e.g., by vacuum methods. At a high rate of vaporization, solid or liquid particles may become entrained in the vapor. It is not necessary to distinguish between liquid and solid particles as both have the same deleterious effect when present in the form of splatter upon a substrateSeveral methods of avoidingthe splatter problem have been attempted in the past. Many prior art devices and methods, however, may not be successfully employed to generate metal vapor that is completely free of included particles nor to generate metal vapor at a controllable high rate suitable for commercial plating of steel strip, for example;

The following prior art patents are representative:

SUMMARY OF THE INVENTION It is an object of the present invention to provide apparatus and method for vaporizing molten metal with elimination of particles in the generated metal vapor.

' Another object is to provide apparatus for coating a continuously moving substrate with metal vapor at a controllable and high rate of production. More particularly, an object of the invention is to provide apparatus for coating a moving steel strip with zinc vapor devoid of splatter.

To theseand other ends, the present invention contemplates metal vaporizing apparatus and method in which molten metal is formed into a thin semi-cylindrical shell having a horizontally disposed central axis. The thin shell communicates with and is supplied from a body of metal. Heating thethin shell of molten metal under vacuum produces metal vapor. The metal vapor generated is directed againsta substrate to be coated.

In one embodiment of the invention a first cylinder memberis charged with a pool of molten metal. The first cylinder member has its central axis disposed horizontally and has at least one passage extending therethrough. A second or outer cylinder member with its central axis=disposed horizontally encloses the first cylinder member and receives'rnolten metal through the passage in the first cylinder member so as to form a thinsemi-cylindrical shell of moltenmetal between the cylinder members. As the thin shell of molten metal remains fixed in size, there is alwaysa constantsupply of molten metal between the cylinder members for vaporization. Preferably, each of the cylinder members as well as the other elements of the system are fabricated of graphite when the molten metal is zinc, sincegraphite is not attacked (neither corroded by nor reactivewith) by zinc.

The first or inner cylinder member is cut away in its top portion so that meansdefining a tortuous path for removing any particles in the generated vapor may be disposed in that area. An outlet removes the generated vapor after it has passed through the tortuous path and includes a nozzle for directing the vapor against a moving substrate to be coated.

In another embodiment of the invention an evaporator member defining an evaporation chamber is employed. The molten metal is disposed in the lower portion of the chamber where it is heated togenerate metal vapor. A shelf extends horizontally across and divides the chamber, although the shelf is provided with a passage to allow the metal vapor to pass therethrough. In one form of this embodiment the shelf is tilted downwardly toward one end of the chamber and a portion of the shelf is recessed about an aperture to collect liquid droplets removed from the metal vapor and to direct them back to the pool of molten metal.

In the upper portion of the chamber above the shelf is located means defining a tortuous path to remove liquid droplets from the metal vapor. The tortuous path preferably includes plural baffles located between the passage in the shelf and the outlet from the chamber. These baffles may be either disposed longitudinally of the chamber or transversely thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional side view of representative apparatus in accordance with the present invention.

FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1.

FIG. 3 is a perspective view of a modified form of representative apparatus in accordance with the present invention and similar to the apparatus of FIG.

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 3.

FIG. 5 is a perspective view of another form of representative apparatus in accordance with the present invention similar to the apparatus of FIG. 1.

representative apparatus similar to the embodiment of FIG. 7.

DETAILED DESCRIPTION Referring to FIG. 1 of the drawings, there is shown a shell in which metal vaporizing apparatus 12 in accordance with one embodiment of the invention is disposed. The shell 10 is fabricated of stainless steel or the like and is maintained under vacuum during vaporization so that metal vapor may be produced under vacuum. The shell 10 is disposable within a furnace 14 so that the shell and hence the metal vaporizing apparatus 12 may be heated to a temperature suffici'ent to vaporize molten'm'etal. In operation, the shell '10 should be capableof withstanding a vacuum of about 0.1 to 1.0 microns and a temperature of about l,500 to 1,800 F. It should be understood that the furnace 14 may be of any suitable type, such as electrical resistance heating of graphite rods, furnace heater tubes enclosing burning gas, or the like. Insulation material 16 is preferably disposed at all openings into the shell 10, while the shell itself is surrounded by refractory material 17 comprising the furnace 14.

Metal vaporizing apparatus 12 may substantially fill the volume of the shell 10.

Two major embodiments of the present invention are detailed in this application. More than one form of each embodiment is described. The embodiments have in common a cylinder member having its central axis disposed horizontally for containing a pool of molten metal. Means defining a tortuous path separated from the area of vaporization are included so that any liquid droplets may be removed from the generated metal vapor before leaving the evaporationchamber. The generated metal vapor exits from the chamber in a horizontal direction so that it may be readily deposited on a continuously vertically moving substrate to form a coating thereon.

FIGS 1 and 2 In a first embodiment of the present invention (see for examples FIGS. 1 and 2) metal vaporizing apparatus 12 includes an outer evaporator cylinder member 18 in which molten metal is vaporized in a vaporization area 19. At one end of the outer evaporator cylinder 18 is disposed a base 20 in which there is located a reservoir 22 which provides molten metal for vaporization. The outer evaporator cylinder 18 and the base 20 are the major exterior elements of metal vaporizing apparatus 12. The entire metal vaporizing apparatus 12 including the base 20 is preferably fabricated of graphite or the like when the molten metal is zinc. Although it is possible to transfer molten metal directly into the reservoir 22, especially in a commercial installation, it is presently contemplated to locate an ingot of metal or metal granules within the reservoir 22 so that upon heating of the shell 10 the ingot or granules will melt to form fluid metal. A cover 23 is provided to maintain the molten metal within the reservoir 22. The end of the cylinder 18 opposite the base 20 is sealed by a plate 24. Vapor and liquid leakage are thus prevented. As the outer evaporator cylinder 18 is cylindrical in shape, having its central axis disposed horizontally, a plurality of supporting elements 25 are provided between the cylinder 18 and the shell 10.

At the bottom portion of the reservoir 22 is a passage 26 extending through the base 20. After the metal has been melted, the molten metal contained in the reservoir 22 is permitted to flow through the passage 26 into the vaporization area 19 of the metal vaporizing apparatus 12. The passage 26, however, is blocked bya valve 28 which either allows or prevents molten metal from leaving the reservoir 22. Normally, the valve 28 is in closed position until the metal ingots or granules within the reservoir 22 have melted and until the tern-v perature of the metal vaporizing apparatus 12 has reached the desired level-The valve 28 is variably controllable and may be of the type disclosed in Iezzi .et al. application,-Ser. No. 778,609, filed'Nov. 25, 1968, entitled Graphite Variable Control Valve-"and assigned to the assignee of the present application. Thus, the valve 28 comprises a valve body 30, an operator structure (not shown) which may be either manual or automatic, and an aperture 32 in the valve body alignable with the passage 26 upon movement of the valve body 30 by the operator structure. In FIG. 1, the valve 28 is shown in open position. As the valve 28 is fabricated of a material non wetted by the molten metal, e.g. graphite when the molten metal is zinc, a liquid-to-liquid seal may be achieved about the valve body 30 so that there will be no liquid leakage through the various clearances about the valve components.

When the aperture 32 is aligned with the passage 26, molten metal may flow from the reservoir 22 through the passage 26 and the aperture 32 into the vaporization area 19 of metal vaporizing apparatus 12. The vaporization area 19 is defined by the outer evaporator cylinder 18 and an inner cylinder member 34 disposed within the outer evaporator cylinder 18. The upper portion of the inner cylinder 34 may be cut away so that it is substantially semi-circular in shape, for purposes explained more fully below. The inner cylinder 34 is also fabricated of graphite or the like when the molten metal is zinc. Graphite has been found to be a suitable material for fabricating the evaporator cylinders 18, 34 as well as the other elements of metal vaporizing apparatus 12 as it does not react with molten zinc, is easily fabricated, maintains its strength at high temperatures, and is efficient in conducting heat from the furnace 14 to the molten zinc to be vaporized. The inner cylinder 34 may be continuously charged with molten metal from the reservoir 22 so that a constant supply of metal vapor may subsequently be generated.

In the bottom portion of inner cylinder 34 are located a plurality of passages 38. Although a pool of molten metal 39 is formed in the inner cylinder 34, a portion of that pool of molten metal is permitted to flow through the passages 38 into the space between the cylinders 18 and 34. Thus, a thin semi-cylindrical shell of molten metal 40 forms between outer wall34a of the innerevaporator cylinder 34, andthe inner wall 18a of the outer evaporator cylinder 18. The depth of themolten metal inithe thin shell40 is generally the same as the depth of the pool ofmolten metal 39 remaining within the inner evaporator cylinder 34. However, the thin shell of liquid boils,an d the distinction between ,vaporand liquidphasesas well asfluid level may be difficult to perceive. Providing a thin semi-cylindrical shell of molten'fl uid allows a-uniform evaporation rate to be achievedasthe volume ofthe thin shell of fluid metal may-be substantially constant. Preferably,the passages38 are uniformiin size andextend in a single row along ,thebottom portion of the inner cylinder 34. It is of course possible to ,use any combination orsiz e of passages 38 S0 longasa .thin

fluid movement through the thin shellof fluid .40. Thus,

vaporization of the molten metal may occurat a high rate so that the apparatus maybe used for commercial coating of continuously moving strip material or the like.

The vaporization rate of molten metal depends primarily on four factors. First, the most critioal, is the temperature of the evaporator, as the vapor pressure of the metal depends on temperature. The second and third factors are the liquid-vapor interface area and the 2, thetortuouspathstructurefor removing droplets entrained in ,themetal vapor in that embodiment comprisesin part an outlet tube 41 which. extends horizontally in .the upper portions of the outer evaporator cylinder 18 andtthesemi-cylindrical innercylinder 34.

The outlet -.tube,4l, .which may also befabricated .of graphitewhenzthe moltenmetallis zinc, hasa plurality of perforations .42 therein through which the vapor passes to befrernoved fromthe vaporizing apparatus 12.

-P,referably,theperforations 42 areof uniform size and are formed'in asingle row atthe bottom .of the outlet tube 41,although-perforations may also be. atthetop of :the tube. ,Generated metal vapor emanating :from the thin shell ofmolte'n metall40 must firstrise past the top edges of'thesemiacylindrical inner cylinder 34, then flow downwardlypast the exterior of outlet tube 41,

and finally flow upwardly through the perforations 42 into the outlettube 41, asbest seenlin FIG. 2. I

The outlet tube 41also serves the function of a nozzle for directing the metal vapor after it has passed through the tortuous path horizontally from the vaporizing apparatus 12. In this case theoutlet tube4l must bfi-SllffiCiGllt :insize to permit ready transport of the vapor from the evaporator cylinders 18, 34. The outlet ,tube 41, whichcontains no perforations 42.along its length in the portion 41a extending beyond the .cylinder=l 8,.directs the metal vapor against a moving liquid-evaporator contact area. Generally, the higher the temperature of the vaporizing apparatus 12, the higher the vaporization rate. However, although the vaporization rate remains constant for a period of time,

it tends to decay when the amount of molten metal in the chamber 28 begins to fall, even though the temperature of the vaporizing apparatus 12 reaches an extremely high level, i.e., about 1,800 F., since the second and third factors are now influencing the evaporation rate. The fourth factor affecting the vaporization rate is the provision ofadequate vapor transport from the vaporizing apparatus 12. If excessive pressure drops exist in the vapor stream causing the pressure to rise in the evaporator, the temperature of the molten metal will rise and the evaporation rate will drop.

After the semi-cylindrical thin shell of fluid metal has been heated to generate metal vapor by the furnace 14, the metal vapor accumulates in the upper portion of the outer cylinder 18. As the inner cylinder 34 has its upper portion cut away, any small amount of vapor generated upon direct heating of the pool of molten metal 39 contained therein also rises to the upper portion of the outer cylinder 18.

Located within the upper portions of the two evaporator cylinders is a structure defining a tortuous path. The metal vapor generated passes through the tortuous path when exiting fromthe vaporizing apparatus 12 so that any droplets entrained in the metal vapor are removed therefrom. As shown in FIGS. 1 and substrate .(not shown typically moving vertically) so that the v por condenses to form a coating thereon.

The shell 10 preferably encases the entire metal vaporizing apparatus 12 including the extension of the outlettube41 which serves as a nozzle, so that no pressure leakage will occur in the system. As the metal vapor is generated at a rapid and controllable rate, a coating of substantially equal thickness may be deposited about the surface .area of the continuously moving substrate.

EXAMPLE 1 Using representative apparatus of the type shown in FIGS. 1 and 2, a zinc ingot weighing 12 lbs. was disposed in the reservoir 22. The metal vaporizing apparatus 12 was located in a stainless steel shell 10, which was then placed in a furnace 14 of the gas burner type. The shell 10 was evacuated to a pressure of about 1 micron and heated to a control temperature of about 1,750 F. (The control temperature is actually the lowest temperature on the steel shell in the evaporation area.) A pressure below 30 microns is preferred to obtain a bright coating. The zinc ingot in the reservoir 22 reached a temperature of about l,l00 F. (l,200 F. temperature of the reservoir itself) which was sufficient to melt the zinc. When the valve 28 was opened, the molten zinc metal flowed into the inner evaporator cylinder 34 to form a pool of molten metal 39 therein. A 54-inch thin shell of molten zinc metal 40 was subsequently formed between the inner and outer evaporator cylinders 18, 34. In the run of the apparatus although the stainless steel shell 10 was heated to a control temperature of l,750 F., the steady-state temperature of the vaporizingapparatus l2 beforeliquid zinc was introduced into the vaporization area 19 was also about 1,750 F., while the steady-state temperature of the vaporization area after the molten zinc metal was introduced was l,680 F.

Five hundred feet of 6-inch wide steel strip were coated with the generated zinc vapor. Previously, however, the steel strip, which was 0.015 inches thick, had been cleaned with an alkali cleaner, pickled in a percent hydrochloric acid solution and electroplated with a copper coating 5 to 7 micro-inches thick to promote adherence of the coating. The strip was maintained at a temperature of about 80 F. and a coating of about 1 mil in thickness was deposited thereon when the strip moved at a rate of about 60 to 75 ft. per minute. The outlet tube 41 was l-inch in diameter. The average condensation rate upon the steel strip was 0.70 lbs. per minute, while the maximum condensation rate was 0.95 lbs. per minute.

It has been determined, however, that the maximum feasible temperature any place on the stainless steel shell 10 should be about l,750 F. in order to avoid collapsing or weakening of the shell structure. Under these limitations a similarly prepared steel strip was coated. The control temperature of the stainless steel shell 10 was 1,480": F. and the average temperature about l,530 F. The steady-state temperature of the vaporizing apparatus 12 before introduction of the molten zinc metal was about l,480 F. while the steady-state temperature of the vaporizing apparatus 12 after introduction of the molten zinc was 1,420 F. The perforations 42 in the outlet tube 41 faced toward the bottom of the outer evaporator cylinder 18. In this run the average condensation rate upon the steel strip was 0.30 lbs. per minute while the maximum condensation rate was 0.56 lbs. per minute. In both runs very little splatter occurred in the coating on the substrate and the coating appearance was considered to be excellent.

FIGS. 3 and 4 A modification of the embodiment of FIG. 1 is shown in FIGS. 3 and 4. A similar inner cylinder member 34' is disposed in a similar outer evaporator cylinder 18' such that a thin shell of fluid metal 40' may form between the cylinders from the pool of molten metal 39' through the passages 38'. However, the apparatus of FIGS. 3 and 4 differs from the apparatus of FIGS. 1 and 2 in that baffles 44 are located at the top portions of the semi-cylindrical inner cylinder 34 and in that no outlet tube 41 is provided for removing generated metal vapor from the vaporizing apparatus 12. The baffles 44 extend throughout the interior of the inner cylinder'34' so that generated metal vapor rising from the pool of molten metal 39 will first strike the baffles.

As apertures 45 are formed between the baffles and the top of the inner cylinder 34', vapor rising from the thin shell of fluid metal 40 will pass through the apertures 45 and beneath the baffles 44 before exiting from the vaporizing apparatus 12'. The baffles 44 may also be fabricated of graphite when the metal vapor is zinc vapor.

To remove the generated vapor from the vaporizing apparatus 12' an aperture 46 is provided in plate 24' which defines an end wall of the cylinders 18, 34. As the apparatus may not entirely remove splatter from the generated vapor, it is preferred that an additional disengagement section 48 be provided adjacent the plate 24' at the end of the metal vaporizing apparatus 12'. The disengagement section 48 comprises a cylindrical section 50 fixed to the plate 24' into which metal vapor is charged through the aperture 46. Within the cylindrical section 50 are disposed a plurality of semicircular bafile plates 52 spaced apart along the length of the section 50 and alternately afiixed to the top and bottom portions of the cylindrical section 50. The semicircular baffle plates 52 are each slightly greater than 180 in circumference so that vapor may not pass through the disengagement section 48 in a direct path. Instead, the metal vapor must follow a tortuous path over each baffle plate 52 affixed to the bottom of the cylindrical section 50 and under each baffle plate 52 affixed to the top of the cylindrical section 50. It is also possible for the baffle plates 52 to be affixed to the cylindrical section 50 at alternate sides thereof, such that the metal vapor must follow a tortuous path around each baffle. The baffle plates 52 may be fabricated of graphite or the like when the metal vapor is zinc vapor. The entrained droplets removed from the metal vapor collects at the base of the cylindrical section 50 from which it may later be removed.

A nozzle 54 transfers the metal vapor horizontally from the disengagement section 48. The nozzle 54 may be fabricated of the same material as the other elements of the apparatus, e. g., graphite, or could be made of low carbon steel or stainless steel and may be of the type which forms a stream of metal vapor as wide as the substrate to be coated. Thus, the nozzle 54 may direct a wide stream of metal vapor against a continuously moving substrate so that the vapor condenses to form a coating thereon. Of course, any other type nozzle 54 may be employed which is sufficient in size to permit ready transport of the metal vapor from the disengagement section 48.

EXAMPLE 2 Representative apparatus of the type shown in FIGS. 3 and 4 was employed to vaporize molten zinc. About 118 lbs. of 99.99 percent pure zinc were melted in an electric furnace and delivered through a heated tube (not shown) into the metal vaporizing apparatus 12. A

stainless steel-clad tantalum tube heated to about 900 to 1,000 F. was utilized to deliver the molten zinc. A chromium carbide coated carbon steel tube might also be used. The metal vaporizing apparatus 12 was located in the stainless steel shell 10 which in turn was disposed within the furnace 14. The shell 10 was evacuated to a pressure of about 6 microns and heated to a temperature of about l,220 F. The internal temperature of the graphite evaporator cylinder was l,265 F. The temperature of the disengagement section 48 was about l,020 F.

Steel strip about 10 in. wide and 0.015 in. thick was coated with generated metal vapor. The steel strip had previously been cleaned in an alkali cleaner maintained at a temperature of about 165 F., pickled in a 5 percent hydrochloric acid solution at ambient temperature and plated-to a thickness of from 2 to 8 micro-inches (preferably to a minimum of 3 micro-inches) in a sodium cyanide-copper cyanide bath kept at a temperature of F. to promote adherence of the coating. The strip was vapor zinc coated at a speed of about 30 ft. per minute and the temperature of the strip was raised by condensation to about 410 F. The condensation rate of the vapor. on the substrate averaged 0.930 lbs. per minute to a coating thickness of 0.580 02. per sq. ft.

minute. The zinc vapor condensed at an average rateof about 1.21 lbs. per minute to, a thickness of about 1.53 oz. per sq. ft. of substrate.

FIGS. and 6 The device of FIGS. 5 and 6 includes an outer evaporator cylinder 18" enclosing a semi-cylindrical inner cylinder 34". A pool of molten metal 39" may be contained within. the inner cylinder 34" to supply through passages 38? a thin shell of molten metal 40" formed between the corresponding walls of the two cylinders 18'', 34". The modification'of FIGS. 5 and 6 tially only .in the form of outlet tube employed to remove the metal vapor from the apparatus. Thus, an outlet tube 56 is disposed in the upper portion of the outer evaporator cylinder 18", which is the cut-away portion of the inner cylinder 34". The outlet tube 56 is substantially larger than the outlet tube 41 of FIGS. 1 and 2. However, the outlet tube 56 contains a series of perforations 58 only at one end 56a thereof and contains no perforations along the extent of the tube. Although in the figures the perforations 58 are shown in a radial pattern, any spacing is satisfactory so long as adequate. vapor transport from the vaporizing apparatus 12" is provided. The end 56a of the outlet tube 56 terminates adjacent the end of the inner cylinder 34". Thus, the tortuous path of this modification is provided when the metal vapor generated is caused to flow over the top portions of the semi-cylindrical inner cylinder 34" and then toward the end 56a of the outlet tube 56 which contains the perforations 58. If the perforations58 are sufficiently small in diameter, droplets will substantially be removed from the metal vapor as the vapor passes through the perforations and will return to the pool of molten metal 39" contained within the inner-cylinder 34". Again, the outlet tube 56 is preferably fabricated of graphite or the like when the molten metal is zinc.

A nozzle 54' similar to that shown in FIG. 3 may be coupled to the end of the outlet tube 56 opposite the end 56a containing the perforations 58. The nozzle 54' will direct the metal vapor horizontally from the vaporizing apparatus 12" toward a continuously moving substrate where the vapor may condense to form a coating thereon.

EXAMPLE 3 Apparatus of the type shown in FIGS. 5 and 6 was also employed in vaporizing molten zinc to provide a coating for copper-plated steel strip. About 200 lbs. of 99.99 percent pure molten zinc were delivered similarly to the procedure of Example 2 to the inner cylinder 34' which was maintained under a vacuum of about 27 to 40 microns pressure. The temperature of the stainless steel shell 10 was about 1,800 F. while the "differsfrom theapparatus of FIGS. 1 and 2 substaninternal temperature of the graphite evaporator cylinders 18", 34- was about 1,620" to 1,640 F. The zinc vapor condensed upon the substrate at an average rate of about 1.00 to 1.38 lbs. per minute to create a coating about 0.966 to 1.322 02. per sq. ft. in thickness. Copper-platedzsteel strip of the type described in Example 2 reached atemperaturein excess of 400 F. and

was transportedpast the end of the nozzle 54 at a speed of about 20 ft. 'per minute. Adhesion of the coating to the substrate was found to be excellentand no splatter was presentinthe coating.

Pros. 7 and 8 disposed in the lower portion of the evaporator cylinder while means for removing splatter from the generated metal vapor is located in the upperportion of the evaporator cylinder 60. Thus, the vaporization area 60a is separated from the splatter removal area in this embodiment as well. Molten metal may be charged into the lower portion of the evaporator cylinder 60 to form a pool of molten metal 6 l either in'the same manner as explained in connection with the vaporizing apparatus 12 of FIG. 1 or from an external source as described in Example 2. Furthermore, the evaporator cylinder 60 is preferably. fabricated of graphite or the like when the molten metal is zinc, as is the entire vaporizing apparatus 59. Again the entire system is maintained under vacuum to provide for the production of metal vapor under vacuum. The vaporizing apparatus 59 is heated within a shell 10 in a furnace 14 of the same type described above in connection with FIG. 1. The molten metal contained in the lower portion of the evaporator cylinder 60 is therefore also heated in order to generate metal vapor. In this embodiment of the invention a thin shell of molten metal is not heated, to generate metal vapor. It shouldv be noted, however, that it is feasible to form the molten metal into a thin semi-cylindrical shell by placing an inner cylinder (not shown) within the evaporator cylinder 60.

In accordance with this embodiment of the invention a shelf 62 extends horizontally across and divides the evaporator cylinder 60 substantially in half. Beneath the shelf 62 is contained the pool of molten metal 61 to be vaporized in the vaporization area 60a while above the shelf 62 is located structure defining a tortuous 'path for removing droplets from the generated metal droplets removed by the tortuous path may flow back toward the pool of molten metal 61 contained in the lower portion of the evaporator cylinder 60. A number of apertures 64 are located in the shelf 62 so that the droplets removed from the generated metal vapor will pass through the shelf 62. In this regard recesses 62a are formed in the shelf 62 surrounding each of the apertures 64 to collect the liquid flowing on the shelf 62 and direct it through the apertures 64 toward the pool of molten metal 61 where the liquid may be revaporized. Preferably, the shelf 62 is fabricated of graphite or the like when the metal vapor is zinc.

The structure defining the tortuous path contained in the upper portion of the evaporator cylinder 60 for removing splatter from the metal vapor consists of a plurality of baffles 66 disposed transversely to the length of the cylinder. The baffles 66 are spaced along the length of the evaporator cylinder 60 and may either alternate or be formed into pairs. The baffles 66, which may be fabricated of graphite or the like when the metal is zinc vapor, are located in the upper portion of the evaporator cylinder 60, between the passages 64 in the shelf 62 and the outlet from the cylinder 60, each extending verticallyfrom the shelf 62 to the interior wall of the cylinder 60. Each of the baffles 66 is a segment of a circle and may be either slightly smaller or larger than a quarter circle. In the instance whereeach baffle 66 is slightly smaller than a quarter circle, the path followed by the vapor is defined by the gap left between adjacent baffies 66 extending down the center of the upper portion of the evaporator cylinder 60, as shown in FIG. 8. If the baffles 66 are each larger than a quarter circle in size, adjacent baffles 66 will slightly overlap so that generated metal vapor will be caused to follow a tortuous path about the ends of the baffles before leaving the cylinder 60.

A nozzle (not shown) is located adjacent end plate 70 of the evaporator cylinder 60 in communication with an aperture 68 in the end plate. The nozzle must be sufficient in size to permit ready transport of the vapor from the cylinder 60 and serves to direct the metal vapor from the tortuous path horizontally of the evaporator cylinder 60. A nozzle of the type shown in FIG. 3 is preferably employed. The nozzle directs the metal vapor against a continuously moving substrate so that the vapor condenses to form a coating thereon.

EXAMPLE 4 Copper-coated steel strip was coated with zinc vapor by use of apparatus of the type shown in FIGS. 7 and 8. The substrate was of the same type and was prepared in the same manner as described in Example 2. In one run using this apparatus, 134 lbs. of 99.99 percent pure molten zinc were delivered in the manner explained in Example 2 to the evaporator cylinder 60 which was maintained under 'a vacuum of 65 microns pressure. The temperature of the stainless steel shell 10 enclosing the vaporizing apparatus 59 was l,600 F., whereas the temperature within the evaporator cylinder 60 was l,250 F. Zinc vapor condensed on a moving strip at an average rate of about 1.71 lbs. per minute to a thickness of about 0.820 oz. per sq. ft. The strip, which reached a temperature of 500 F., moved at a speed of about 40 ft. per minute. There was perfect adhesion of the zinc coating to the strip and no splatter was present in the coating. The splatter problem was minimized by minimizing the temperature difference between the evaporator cylinder 60 and the molten metal delivered to the'cylinder.

In another run employing apparatus of the type shown in FIGS. 7 and 8 similar steel strip was vapor coated with zinc metal vapor produced from 2 I 5 lbs. of molten zinc. During this run the temperature of the stainless steel shell 10 was about l,700 F. The pressure within the evaporator cylinder 60 was about 30 to 35 microns while the internal temperature of the evaporator cylinder 60 was about l,270 F. About 3.24 lbs. per minute of zinc vapor condensed on a moving substrate (strip) to a thickness of about 0.890 oz. per sq. ft. The strip moved at about ft. per minute and reached a temperature of about 450 F.

FIG. 9

A modification of the embodiment of FIGS. 7 and 8 is shown in FIG. 9. Vaporizing apparatus 59 includes an evaporator cylinder '60 in which a pool of molten metal 61' is disposed for vaporization in a vaporization area 60a. A shelf 62' extends horizontally across and divides the evaporator cylinder, 60' into upper and lower portions. In the upper portion of the cylinder 60' is located structure defining a tortuous path for removing droplets from the generated metal vapor. Thus, vaporization and droplet removal occur inv separate locations. The difierence between the embodiment of FIGS. 7 and 8 on one hand and the form shown in FIG. 9 on the other hand is that, in the vaporizing apparatus 59 of FIG. 9, the tortuous path extends longitudinally of the evaporator cylinder 60' rather than transversely thereto. The shelf 62 again does not extend along the entire length of the evaporator cylinder 60' so that the generated metal vapor emanating from the pool of molten metal 61 may pass around the end of the shelf to enter the tortuous path. Also, the shelf 62' may be tilted downwardly toward one end of the evaporator cylinder 60 and may include plural apertures 72 therein whereby droplets removed from the metal vapor by the tortuous path structure will flow down the shelf 62 and be directed back to the pool of molten metal 61'. Again the entire vaporizing apparatus 59 may be fabricated of graphite when the metal is zinc.

In the upper portion of the evaporator cylinder 60' of FIG. 9 there is an outlet tube 74. The outlet tube 74, which may be fabricated of graphite or the like when the metal vapor is zinc, extends along the length of the evaporator cylinder 60' on the shelf 62'. A plurality of uniform perforations 76 preferably are spaced along the length of the outlet tube 74 and preferably also are directed toward the upper portion of the evaporator cylinder 60'. Although the outlet tube 74 and the shelf 62' form a tortuous path about which the metal vapor must pass to leave the vaporizing apparatus 59, baffles 78 may be affixed additionally to the side of the outlet tube 74. These baffles 78, which may be graphite when the metal vapor is zinc vapor, extend along the entire length of the outlet tube 74 and are directed toward the upper portion of the evaporator cylinder 60'. The tortuous path is thus completely defined as following the end of the shelf 62 around which the generated metal vapor must pass, the ends or tops of the baffles 78, and the perforations 76 in the outlet tube 74. The entrained droplets removed from the metal vapor by the tortuous path structure will flow back along the shelf 62 and be directed through the apertures 72 into the pool of molten metal 61 Generated metal vapor is removed from the evaporator cylinder 60' by passing through the perforations 76 substrate so that the vapor condenses toform a coating thereon.

EXAMPLE Using representative apparatus of the type shown in FIG. 9, about 35 lbs. of extremely pure zinc were fed into the evaporator cylinder 60 by means described in Example 1. The metal vaporizing apparatus 59' was placed in a stainless steel shell which was heated to a temperature of about l,700 F. in a furnace 14. The shell 10 was evacuated toa pressure of about 1 micron. The temperature of the evaporator cylinder60 before introduction of the molten zinc was about .l,700 F. while the temperature of the cylinder afterintroduction of the molten zinc was about 1,500F. A Z-inchoutlet tube 74 was employed to remove the generated vapor from the evaporator cylinder 60'. Copper-plated steel strip of the type used in Example 1 was plated (about 0.5 to 1.0 mils in thickness) at an average condensation rate of about 0.49 lbs. per minute, the maximum condensation rate being about 0.74 lbs. per minute.

Thus, the present invention provides for vaporization of molten metal, particularly zinc, without entrainment of a substantial amount of droplets in the metal vapor. The invention further provides for the coating of a substrate, particularly copper-plated steel. strip with a metal vapor at a high rate of production and at'a controllable rate so that a coating of unifonn thickness may be deposited on the continuously moving substrate.

We claim:

1. Apparatus for vaporizing molten metal, comprismg:

a. a first cylinder member with its central axis disposed horizontally for receiving and displacing a pool of molten metal and having at least one passage extending therethrough;

b. a second cylinder member with its central axis disposed horizontally enclosing said first cylinder member and adapted to receive molten metal through said passage from said first cylinder member to form a thin semi-cylindrical shell of molten metal between said cylinder members; and

c. means for heating said thin shell of molten metal to generate metal vapor.

2. Apparatus according to claim 1, including means for continuously charging said first cylinder member with molten metal.

3. Apparatus according to claim 2, wherein said charging means comprises:

a. a reservoir for containing a supply of molten metal and having an outlet therefrom in communication with said first cylinder member; and

b. valve means for controlling the flow of molten metal through said outlet from said reservoir to said first cylinder member.

4. Apparatus according to claim 1, including means for maintaining said cylinder membersunder vacuum to provide for the production of metal vapor under vacuum.

5. Apparatus according to claim 1, wherein said cylinder members are fabricated of graphite when said moltenmetal is zinc. i

6. Apparatus according to claim 1, further comprising means disposed in said cylinder members and defining a tortuous path for removing liquid droplets from said generated vapor.

7. Apparatus accordingto claim 1, wherein said first cylinder member is open at the top portion thereof so that it is semi-cylindrical in shape.

8. Apparatus according to claim 7, further comprising outlet means extending horizontally in said first cylinder member in the open portion thereof for removing said generated vapor therefrom.

9. Apparatu s according to claim. 8, wherein said outlet means comprises a tube having a plurality of perforations therein through which saidvapor may pass to be removed from said cylinder members.

10. Apparatus according to claim 1, further comprising a nozzle extending horizontally from said cylinder members. r p

1 1. Apparatus according to claim 1, including means for directing said generated metal vapor against a continuously moving substrate to be coated.

12. Apparatus for vaporizing molten metal, comprismg:

a. an evaporator member for containing a pool of molten metal in the lower portion thereof which is heated to generate metal vapor;

'. a shelf extending horizontally across and dividing said evaporator member into distinct compartments communicating with each other only by a passage extending through said shelf through which metal vapor may pass;

c. means in the upper portion of said evaporator member above said shelf and defining a tortuous path to remove liquid droplets from said metal vapor which may pass through said passage;

d. outlet nozzle means extending from said upper portion of said evaporator member for removing said generated vapor therefrom and applying said vapor to a substrate to be coated; and

e. means for heating said evaporator member portions to generate metal vapor for deposition upon said substrate.

13. Apparatus for vaporizing molten metal, comprisa. an evaporator member for containing a pool of molten metal in the lower portion thereof which is heated to generate metal vapor;

. a shelf extending horizontally across and dividing said evaporator member and having a passage extending therethrough through which metal vapor may pass, said shelf being tilted downwardly toward one end of said evaporator member;

c. means in the upper portion of said evaporator member above said shelf and defining a tortuous path to remove liquid droplets from said metal vapor which may pass through said passage;

d. outlet nozzle means extending from said upper portion of said evaporator member for removing said generated vapor therefrom and applying said vapor to a substrate to be coated; and

e. means for heating said evaporator member portions to generate metal vapor for deposition upon said substrate.

14. Apparatus for vaporizing molten metal, comprisa. an evaporator member for containing a pool of molten metal in the lower portion thereof which is heated to generate metal vapor;

. a shelf extending horizontally across and dividing said evaporator member and having a passage extending therethrough through which metal vapor may pass, a portion of said shelf being recessed to collect droplets removed from said metal vapor and direct them to said pool of molten metal;

c. means in the upper portion of said evaporator member above said shelf and defining a tortuous path to remove liquid droplets from said metal vapor which may pass through said passage;

d. outlet nozzle means extending from said upper portion of said evaporator member for removing said generated vapor therefrom and applying said vapor to a substrate to be coated; and

e. means for heating said evaporator member portions to generate metal vapor for deposition upon said substrate.

15. Apparatus for vaporizing molten metal, comprisa.'an evaporator member for containing a pool of molten metal in the lower portion thereof which is heated to generate metal vapor;

. a shelf extending horizontally across and dividing said evaporator member and having a passage extending therethrough through which metal vapor may pass;

c. means in the upper portion of said evaporator member above said shelf and defining a tortuous path to remove liquid droplets from said metal vapor which may pass through said passage, said tortuous path means including plural battles between said passage in said shelf and the outlet means of ((1) below;

d. outlet nozzle means extending from said upper portion of said evaporator member for removing said generated vapor therefrom and applying said vapor to a substrate to be coated; and

e. means for heating said evaporator member portions to generate metal vapor for deposition upon said substrate.

16. Apparatus according to claim 15, wherein said baffles are disposed longitudinally of said evaporator member within said upper portion thereof.

17. Apparatus according to claim 15, wherein said bafi'les are disposed transversely in said upper portion of said evaporator member.

18. Apparatus according to claim 12, wherein said outlet means extendsthroughout the length of said evaporator member.

19. Apparatus for vaporizing molten metal, comprismg:

a. an evaporator member for containing a pool of molten metal in the lower portion thereof which is he te to en ate metal va or; b. a s e f exen ing horizontally across and dividing said evaporator member and having a passage extending therethrough through which metal vapor y p c. means in the upper portion of said evaporator member above said shelf and defining a tortuous path to remove liquid droplets from said metal vapor which may pass through said passage;

d. outlet nozzle means extending from said upper portion of said evaporator member for removing said generated vapor therefrom and applying said vapor to a substrate to be coated, said outlet means extending throughout the length of said evaporator member and comprising a tube having a plurality of perforations therein through which said generated vapor may pass to be removed from said evaporator member; and

tions to generate metal vapor for deposition upon said substrate.

20. Apparatus according to claim 12, including means for maintaining said evaporator member under vacuum to provide for the production of metal vapor under vacuum.

21. Apparatus according to claim 12, wherein said evaporator member, said shelf and said tortuous path means are fabricated of graphite when said molten metal is zinc.

22. Apparatus for vaporizing molten metal, comprismg:

a. first and second concentric cylinder members with their central axes horizontally disposed, said cylinder members being spaced apart to define a space therebetween;

b. means for supplying molten metal to said space, said molten metal constituting a semi-cylindrical thin shell of metal in said space;

c. means for heating said thin shell of molten metal to vaporize it;

d. means for maintaining said thin shell under vacuum to provide for the production of metal vapor under vacuum; and

e. means for directing the metal vapor against a substrate to be coated.

. means for heating said evaporator member por- 

1. Apparatus for vaporizing molten metal, comprising: a. a first cylinder member with its central axis disposed horizontally for receiving and displacing a pool of molten metal and having at least one passage extending therethrough; b. a second cylinder member with its central axis disposed horizontally enclosing said first cylinder member and adapted to receive molten metal through said passage from said first cylinder member to form a thin semi-cylindrical shell of molten metal between said cylinder members; and c. means for heating said thin shell of molten metal to generate metal vapor.
 2. Apparatus according to claim 1, including means for continuously charging said first cylinder member with molten metal.
 3. Apparatus according to claim 2, wherein said charging means comprises: a. a reservoir for containing a supply of molten metal and having an outlet therefrom in communication with said first cylinder member; and b. valve means for controlling the flow of molten metal through said outlet from said reservoir to said first cylinder member.
 4. Apparatus according to claim 1, including means for maintaining said cylinder members under vacuum to provide for the production of metal vapor under vacuum.
 5. Apparatus according to claim 1, wherein said cylinder members are fabricated of graphite when said molten metal is zinc.
 6. Apparatus according to claim 1, further comprising means disposed in said cylinder members and defining a tortuous path for removing liquid droplets from said generated vapor.
 7. Apparatus according to claim 1, wherein said first cylinder member is open at the top portion thereof so that it is semi-cylindrical in shape.
 8. Apparatus according to claim 7, further comprising outlet means extending horizontally in said first cylinder member in the open portion thereof for removing said generated vapor therefrom.
 9. Apparatus according to claim 8, wherein said outlet means comprises a tube having a plurality of perforations therein through which said vapor may pass to be removed from said cylinder members.
 10. Apparatus according to claim 1, further comprising a nozzle extending horizontally from said cylinder members.
 11. Apparatus according to claim 1, including means for directing said generated metal vapor against a continuously moving substrate to be coated.
 12. Apparatus for vaporizing molten metal, comprising: a. an evaporator member for containing a pool of molten metal in the lower portion thereof which is heated to generate metal vapor; b. a shelf extending horizontally across and dividing said evaporator member into distinct compartments communicating with each other only by a passage extending through said shelf through which metal vapor may pass; c. means in the upper portion of said evaporator member above said shelf and defining a tortuous path to remove liquid droplets from said metal vapor which may pass through said passage; d. outlet nozzle mEans extending from said upper portion of said evaporator member for removing said generated vapor therefrom and applying said vapor to a substrate to be coated; and e. means for heating said evaporator member portions to generate metal vapor for deposition upon said substrate.
 13. Apparatus for vaporizing molten metal, comprising: a. an evaporator member for containing a pool of molten metal in the lower portion thereof which is heated to generate metal vapor; b. a shelf extending horizontally across and dividing said evaporator member and having a passage extending therethrough through which metal vapor may pass, said shelf being tilted downwardly toward one end of said evaporator member; c. means in the upper portion of said evaporator member above said shelf and defining a tortuous path to remove liquid droplets from said metal vapor which may pass through said passage; d. outlet nozzle means extending from said upper portion of said evaporator member for removing said generated vapor therefrom and applying said vapor to a substrate to be coated; and e. means for heating said evaporator member portions to generate metal vapor for deposition upon said substrate.
 14. Apparatus for vaporizing molten metal, comprising: a. an evaporator member for containing a pool of molten metal in the lower portion thereof which is heated to generate metal vapor; b. a shelf extending horizontally across and dividing said evaporator member and having a passage extending therethrough through which metal vapor may pass, a portion of said shelf being recessed to collect droplets removed from said metal vapor and direct them to said pool of molten metal; c. means in the upper portion of said evaporator member above said shelf and defining a tortuous path to remove liquid droplets from said metal vapor which may pass through said passage; d. outlet nozzle means extending from said upper portion of said evaporator member for removing said generated vapor therefrom and applying said vapor to a substrate to be coated; and e. means for heating said evaporator member portions to generate metal vapor for deposition upon said substrate.
 15. Apparatus for vaporizing molten metal, comprising: a. an evaporator member for containing a pool of molten metal in the lower portion thereof which is heated to generate metal vapor; b. a shelf extending horizontally across and dividing said evaporator member and having a passage extending therethrough through which metal vapor may pass; c. means in the upper portion of said evaporator member above said shelf and defining a tortuous path to remove liquid droplets from said metal vapor which may pass through said passage, said tortuous path means including plural baffles between said passage in said shelf and the outlet means of (d) below; d. outlet nozzle means extending from said upper portion of said evaporator member for removing said generated vapor therefrom and applying said vapor to a substrate to be coated; and e. means for heating said evaporator member portions to generate metal vapor for deposition upon said substrate.
 16. Apparatus according to claim 15, wherein said baffles are disposed longitudinally of said evaporator member within said upper portion thereof.
 17. Apparatus according to claim 15, wherein said baffles are disposed transversely in said upper portion of said evaporator member.
 18. Apparatus according to claim 12, wherein said outlet means extends throughout the length of said evaporator member.
 19. Apparatus for vaporizing molten metal, comprising: a. an evaporator member for containing a pool of molten metal in the lower portion thereof which is heated to generate metal vapor; b. a shelf extending horizontally across and dividing said evaporator member and having a passage extending therethrough through which metal vapor may pass; c. means in the upper portion of said evaporator member above said shelf and defining a tortuous path to remOve liquid droplets from said metal vapor which may pass through said passage; d. outlet nozzle means extending from said upper portion of said evaporator member for removing said generated vapor therefrom and applying said vapor to a substrate to be coated, said outlet means extending throughout the length of said evaporator member and comprising a tube having a plurality of perforations therein through which said generated vapor may pass to be removed from said evaporator member; and e. means for heating said evaporator member portions to generate metal vapor for deposition upon said substrate.
 20. Apparatus according to claim 12, including means for maintaining said evaporator member under vacuum to provide for the production of metal vapor under vacuum.
 21. Apparatus according to claim 12, wherein said evaporator member, said shelf and said tortuous path means are fabricated of graphite when said molten metal is zinc.
 22. Apparatus for vaporizing molten metal, comprising: a. first and second concentric cylinder members with their central axes horizontally disposed, said cylinder members being spaced apart to define a space therebetween; b. means for supplying molten metal to said space, said molten metal constituting a semi-cylindrical thin shell of metal in said space; c. means for heating said thin shell of molten metal to vaporize it; d. means for maintaining said thin shell under vacuum to provide for the production of metal vapor under vacuum; and e. means for directing the metal vapor against a substrate to be coated. 